The present invention relates to a resin-encapsulation semiconductor device using a lead frame and a method for fabricating the same. More particularly, it relates to a resin-encapsulation semiconductor device in which a die pad for mounting a semiconductor element is exposed from an encapsulation resin and a method for fabricating the same, and furthermore, it relates to a thin and highly reliable resin-encapsulation semiconductor device in which a semiconductor element with a large package area ratio can be packaged and a method for fabricating the same.
Recently, in order to cope with downsizing of electronic equipment, semiconductor components such as a resin-encapsulation semiconductor device are required to have a high packaging density. Also in accordance with the downsizing, the semiconductor components have become small and thin. Furthermore, the semiconductor components are required to have a multi-pin structure in spite of their compactness and small thickness, and there is a demand for a compact and thin resin-encapsulation semiconductor device with a high density.
Now, a conventional resin-encapsulation semiconductor device with an exposed die pad will be described with reference to FIGS. 8A through 8C. FIG. 8A is a plan view of the conventional resin-encapsulation semiconductor device, FIG. 8B is a bottom view thereof and FIG. 8C is a cross-sectional view thereof taken along line VIIIC-VIIIC′ of FIG. 8B.
As shown in FIGS. 8A through 8C, in the conventional resin-encapsulation semiconductor device, a semiconductor element 102 is mounted on a support 101a formed on a die pad 101 of a lead frame, and the semiconductor element 102 is electrically connected to inner leads 103 through metal wires 104. The resin-encapsulation semiconductor device of FIGS. 8A through 8C has an exposed die pad with the semiconductor element 102 disposed on the die pad 101 and the inner leads 103 encapsulated within an encapsulation resin 105, a side face of the encapsulation resin 105 and the outside edges (ends) of the inner leads 103 are disposed on the same plane, and the bottom of the die pad 101 is exposed from the encapsulation resin 105.
The die pad 101 has the support 101a elevated within its plane, and the support 101a is formed by pressing above a semi-cut plate portion of the die pad 101. In other words, the resin-encapsulation semiconductor device shown in FIGS. 8A through 8C has an upset structure for placing the bottom of the mounted semiconductor element at a higher level than the upper faces of the inner leads 103. Each metal wire 104 connected to the semiconductor element 102 is connected to a portion in the vicinity of a groove 103a formed on the upper face of the inner lead 103.
In the bottom view of FIG. 8B, portions exposed at the respective comers of the encapsulation resin 105 of the package correspond to exposed bases of supporting leads 106 supporting the die pad 101.
Next, a method for fabricating the conventional resin-encapsulation semiconductor device will be described with reference to FIGS. 9A, 9B and 10A through 10D.
FIGS. 9A and 9B show a lead frame for use in the fabrication of the conventional resin-encapsulation semiconductor device. FIG. 9A is a plan view of the lead frame and FIG. 9B is a cross-sectional view thereof taken along line IXB-IXB′ of FIG. 9A. FIGS. 10A through 10D are cross-sectional views for showing procedures in the fabrication of the conventional resin-encapsulation semiconductor device using the lead frame of FIGS. 9A and 9B.
First, the lead frame for use in the fabrication of the conventional resin-encapsulation semiconductor device will be described.
As shown in FIGS. 9A and 9B, the conventional lead frame includes a die pad 101, supporting leads 106 and a plurality of inner leads 103. The die pad 101 has, within its plane, a support 101a provided inside a plate-like outer frame made from a metal plate for mounting a semiconductor element. Each supporting lead 106 supports the die pad 101 at the tip thereof and is connected to the outer frame at the base thereof The tips of the plural inner leads 103 are respectively arranged so as to oppose the sides of the die pad 101, and the bases of the plural inner leads 103 are connected to the outer frame. A plurality of grooves 103a are formed on the upper face of each inner lead, and the tip of each inner lead is tapered. The conventional lead frame has a thickness of approximately 200 through 300 μm.
A plurality of lead frames each having the structure as shown in FIGS. 9A and 9B are continuously formed in a matrix inside one outer frame.
Next, the method for fabricating the conventional resin-encapsulation semiconductor device using this lead frame will be described.
First, as shown in FIG. 10A, the above-described lead frame is prepared. Specifically, the prepared lead frame includes, inside the metal plate outer frame, as shown in FIGS. 9A and 9B, the rectangular die pad 101 having, on the upper face thereof, the support 101a for mounting a semiconductor element; the supporting leads for supporting the die pad 101; and the inner leads 103 in the shape of beams to be electrically connected to the mounted semiconductor element through connecting means such as metal wires.
Next, as shown in FIG 10B, a semiconductor element 102 is bonded onto the support 101a of the die pad 101 of the lead frame with an adhesive such as a silver paste (which procedure is designated as a die bonding step).
Then, as shown in FIG. 10C, each electrode pad (not shown) disposed on the upper face of the semiconductor element 102 mounted on the die pad 101 is connected to an upper portion at the tip of the inner lead 103 of the lead frame through a metal wire 104 (which procedure is designated as a wire bonding step). In this case, the metal wire 104 is connected to a space between the grooves 103a provided on the upper face of the inner lead 103.
Thereafter, as shown in FIG. 10D, the die pad 101, the semiconductor element 102 and the inner leads 103 are encapsulated within an encapsulation resin 105 with an encapsulation sheet adhered onto the bottom of the lead frame.
This procedure is performed so as to individually encapsulate each semiconductor element disposed on the lead frame and not to entirely encapsulate the whole upper face of the lead frame. Also, since the encapsulation sheet is adhered onto the bottom of the lead frame in this procedure, an encapsulated region includes the die pad 101 excluding the bottom thereof, the supporting leads, the semiconductor element 102, the inner leads excluding the bottoms thereof and connecting regions with the metal wires 104, and hence, the bottom of the die pad 101 is exposed from the bottom of the encapsulation resin 105 after the encapsulation.
After the encapsulation, the bases of the supporting leads and the inner leads 103 connected to the outer frame are cut, resulting in obtaining a resin-encapsulation semiconductor device in which the ends (the outside edges) of the supporting leads and the inner leads 103 are disposed on substantially the same plane as the side face of the encapsulation resin 105.
However, the present inventors have found, through examination on the structure of and the fabrication method for the conventional resin-encapsulation semiconductor device, the following: Since the conventional die pad has the elevated support formed by the semi-cut pressing, when a semiconductor element is disposed on the support of the die pad, the entire thickness of the resin-encapsulation semiconductor device is increased by a thickness corresponding to the upsetting extent of the support, which can be a restriction in attaining a desired small thickness. In particular, when a large semiconductor element is packaged, the thickness of the resin-encapsulation semiconductor device is greatly affected, and hence, it is impossible to attain, by using this structure, a small thickness with a large semiconductor element packaged.
Furthermore, the inner leads are encapsulated substantially on the single side, and hence, external impact or stress caused within the encapsulation resin may apply stress to the metal wires connected onto the inner leads, so that there may be fear of break and degradation of the reliability in the connection. In the conventional resin-encapsulation semiconductor device, a plurality of grooves are provided on the upper face of each inner lead and the metal wire is connected to a space between the grooves, so as to cancel or release the applied stress. However, in consideration of the area of each lead included in a small package, it is very difficult to form a plurality of grooves on each inner lead and further secure a bonding area for the connection to a metal wire. In addition, in the resin-encapsulation semiconductor device with the one side encapsulation structure, it is necessary, in accordance with the downsizing of leads, to improve the connection reliability of metal wires.
Also, in the conventional method for fabricating the resin-encapsulation semiconductor device, in particular, in the resin encapsulating procedure, the entire lead frame is not encapsulated but the semiconductor elements disposed within the lead frame are individually encapsulated. Therefore, in order to separate each resin-encapsulation semiconductor device from the lead frame after the encapsulation, it is necessary to cut the lead frame with a mold, which can be an obstacle to improve the fabrication efficiency.
The present invention was devised in consideration of these disadvantages, and a principal object is providing a resin-encapsulation semiconductor device in which a larger semiconductor element is packaged to increase the package area ratio for realizing a CSP (chip size package) while suppressing increase in the thickness of the resin-encapsulation semiconductor device itself, and a method for fabricating the same.